1. Field of the Invention
The present invention relates to mobile telephone systems and, more particularly, to a method for automatically setting the area code for a call in a code division multiple access (CDMA) mobile telephone system.
2. Description of the Related Art
A mobile communication system, such as a Code Division Multiple Access (CDMA) system for Personal Cellular Services (PCS), includes: base station transceiver subsystems (BTSs) for providing services to mobile stations; base station controllers (BSC); a base station management system (BSM) for managing a number of BSCs; a mobile switching center (MSC); and a location register (LR) system.
FIG. 1 is a schematic diagram illustrating the operation of a mobile communication system. A BTS 100 exchanges (transmits and receives) signals and data with a mobile station 200 through an antenna 150. In general, BTS 100 transmits an overhead channel composed of a pilot channel, a sync channel, and a paging channel to mobile station 200 prior to a call set-up. The BTS 100 transmits various types of information to mobile station 200, such as, for example, a pilot PN offset code, a system time, a system identification (ID), a network ID, a paging channel data rate, and a neighbor list.
The BTS 100 recognizes the location and status of mobile station 200 through the overhead channel, so a communication can be immediately established between BTS 100 and mobile station 200. The mobile station 200 transmits a specific frequency channel loading a telephone number to BTS 100 so that BTS 100 can be allocated a channel from a mobile switching center (MSC).
In order to establish a call in a mobile communication system having the above described architecture, the area code number (area code) of the subscriber receiving a call plus a telephone office number including the last four digits should be pressed. For example, when a subscriber who lives in Kumi City (Korea) wants to call his home, he should press 11 digits, such as "0546+123+4567". In the case that the subscriber wants to call a place having a shorter area code (e.g., Seoul City in Korea), he should press 9 digits such as "02+345+6789". However, if a subscriber is using a mobile telephone while driving an automobile or operating machinery, he or she may have an accident by having to press so many digits. In order to overcome the above problem of having to press numerous digits, a recently developed mobile telephone employs a method for storing a frequently used area code in the mobile telephone and using the stored area code when a subscriber makes a call. However, the method is deficient in that a mobile telephone using the method can only store one area code. Thus, if a subscriber wants to use several area codes, he should change the area code for each area to which he belongs and store it in the mobile telephone.
Therefore, as stated above, a maximum of 11 digits should be pressed to establish an out-of-town call from a mobile station in a mobile communication system according to the prior art. Further, even if the mobile station can store an area code, such storage may prove to be of no utility in the case that the location to be called does not correspond to the stored area code. Moreover, when a subscriber who visits at an unfamiliar area needs to make a call but does not know the corresponding area code, determining the area code may prove to be quite an inconvenience.
Another conventional approach to the above problem is disclosed in U.S. Pat. No. 5,732,349, filed on Mar. 24, 1998, and entitled "System and method for controlling a portable telephone according to discriminated area code". A system according to the U.S. Pat. No. 5,732,349 patent stores frequency band information associated with a plurality of areas in which the telephone can be operated and automatically sets an environment for communication according to each area. The system includes: a communication control unit; a memory for storing control information; a receiver for receiving an area signal; and a reading unit for reading a control signal from the memory. The receiver classifies an area code received from the base station. The reading unit reads one of the control signals from the memory in accordance with the area signal using the area code. The communication control unit controls communication through the base station by changing the communication environment of the mobile station in accordance with the control information.
However, the invention of the U.S. Pat. No. 5,732,349 patent is not particularly effective with respect to a CDMA system, since the CDMA system is not deficient with respect to matching frequency bands to corresponding areas. Instead, in the CDMA system, it would be desirable and highly advantageous for a subscriber to be provided with area code information when the subscriber is in a new area.